The present invention relates to a carbon commutator used in, for example, a motor for a fuel pump.
An in-tank type fuel supply pump, in which a motor and a pump are integrally mounted within a fuel tank, is used for supplying fuel to, for example, an automobile. In general, the fuel supply pump of this type is constructed so that the fuel can be moved out of the fuel supply pump from its pump section through the motor housing, and brought into contact with the commutator of the motor. If gasoline containing alcohol is used as a fuel, it is known in the art that copper in that portion of the commutator which is brought into a sliding contact with the brush is corroded by the alcohol contained in the fuel. The corroded copper markedly shortens the life of the pump.
As a commutator taking measures against an alcohol-containing fuel, proposed is a carbon commutator, in which a metal segment is joined to a carbon segment by soldering via a metal plating interposed therebetween, and a brush is brought into a sliding contact with the carbon segment. A commutator of this type is disclosed in, for example, U.S. Pat. No. 5,175,463. However, a motor which equips a carbon commutator may perform poorly because the plating solution permeats through the carbon segment in the plating process. Also, the plating treatment may increase the manufacturing cost. Further, in the subsequent process of welding a coil to the carbon commutator, the solder can be melted and cause peeling or positional deviation of the carbon segment.
Another method to produce a carbon commutator is disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 10-004653. In this method, a projection mounted on the carbon segment is inserted into a hole made in the metal segment so as to join these two segments. However, the projection mounted on the carbon segment only consists of carbon element so that it lacks ductility. Therefore, the projection is readily abraded when inserted into the hole, resulting in failure to join the two segments firmly. JP '653 also teaches an idea that plating solution which is applied to both segments joins them together. However, this measure may also increase the manufacturing cost.